1. Field of the Invention
The present invention relates to an improved transmission type screen which is used in the so-called projection type television having a projector and a screen accommodated in one cabinet and makes it possible to view a clear image with no ghost image or moire following the image, and a Fresnel lens sheet used therein.
2. Description of the Related Art
As a television whose viewing screen size is large, there is the so-called projection type television wherein an image is projected from a rear surface thereof and is watched or viewed from a front surface.
As illustrated in FIGS. 5A and 5B, a conventional projection type television 31 is the one wherein a screen 101 is fitted to a bored window portion at the upper part of its front surface of a cabinet 10; a projector 2 is disposed at a lower position of the interior thereof; and a mirror 3 for making small the depth of the cabinet 10 is disposed at the upper position of its rear surface. Each of these members is disposed in the way of having a positional relationship which permits the projection light 4 from the projector 2 to be reflected by the mirror 3 and projected onto the screen 101, and is received within the same cabinet and fixed. It is to be noted that, for clarifying the interior of the cabinet 10, in each of the illustrations, the side surfaces are removed.
As a screen 101 in the conventional projection type television 31 there is used the one in which, as illustrated in FIG. 6, a Fresnel lens sheet 111 is disposed on the rear surface side, and a lenticular lens sheet 121 is disposed on the watching, or viewing, side, in the way in which the both are located close to each other.
The lenticular lens sheet 121, as one example, has on the rear surface side, i.e. the Fresnel lens sheet 111 side a lenticular lens 122 configured in the way in which a lot of unit lenticular lenses are arrayed so that the direction of the groove defined between each two of the unit lenticular lenses may be in coincidence with the vertical direction of the screen. It has on the viewing side of the lenticular lens sheet 121 and at the position corresponding to a non-condensing portion of the lenticular lens 122 of the rear surface side a light-shading layer 123 for preventing the reflection of a light having entered from the viewing side.
The Fresnel lens sheet 111, as one example, has a Fresnel lens 112 on the viewing side, i.e. the lenticular lens sheet 121 side and has a flat surface 114 on the rear surface side, i.e. the projecting side.
As illustrated in FIG. 7, when a projection light 4 is projected from the rear surface onto the Fresnel lens sheet 111 in the above-described screen 101, this projection light 4 transmits through the Fresnel lens sheet 111 and, in addition, other than this, a reflected light 4a occurs upon the rear surface of the Fresnel lens sheet 111. As illustrated in FIG. 5B, the reflected light 4a reflected by the rear surface of the Fresnel lens sheet 111 is reflected again by the mirror 3 and thereafter enters the screen 101 again. Since this incident light enters the screen at a position different from the initial incident position of the projection light 4, a ghost image occurs at the shifted position in addition to the original image to become a cause of the so-called “ghost”.
Especially, the shorter the length of the optical path between the projector 2 and the screen 101, i.e. the projection distance is, or/and, the shorter the distance between the screen 101 and the mirror 3 is, the more likely to occur the ghost is.
Various kinds of attempts for dissolving the occurrence of ghost have heretofore also been made. According to, among them, the attempt to form an anti-reflection layer on the rear surface of the screen by deposition, or the like, it is indeed possible to weaken the intensity of the ghost but it is impossible to dissolve the ghost. Also, performing deposition with respect to the rear surface of the individual screen results in the poor manufacturing efficiency and so cannot be said to be a technique suitable from the industrial point of view.
Further, in Japanese Patent Application Laid-Open No. 5-158153, the technique is disclosed of providing on the rear surface of the Fresnel lens sheet a configuration of concavities and convexities such as satin, hair line, or lenticular lens and, in this case, providing especially a horizontal lenticular lens configured to get the direction of the grooves oriented in the horizontal direction. By this technique, also, it discloses that such ghost problem can be solved. However, when the lenticular lens sheet is combined with the Fresnel lens sheet, the drawback occurs that, as a result of the lenticular lens being added to the rear surface of the Fresnel lens sheet, the occurrence of moire is furthered.